1. Field of the Invention
The present invention relates to an antimicrobial polymer having a polyorganosiloxane group introduced into the molecule, to a process for its production, to an antimicrobial agent and to a composition comprising the antimicrobial agent and a resin. More specifically, the invention relates to ε-polylysine having a polyorganosiloxane group introduced into the molecule and a process for its production (the ε-polylysine will hereinafter be referred to as “silicone-modified ε-polylysine”), to an antimicrobial agent comprising an amino group-containing antimicrobial polymer having a polyorganosiloxane group introduced into the molecule (the polymer will hereinafter be referred to as “silicone-modified antimicrobial polymer” and the antimicrobial agent will hereinafter be referred to as “silicone-modified antimicrobial agent”), and to a composition comprising the silicone-modified antimicrobial agent and a resin.
2. Related Art
A large assortment of bacteria and molds exist in human living spaces. Such microbes often produce decomposition of foods and generate malodors, resulting in a discomforting environment. They are also responsible for various diseases including food poisoning and dermopathies such as tinea and the like, and in certain cases can even be life threatening to individuals with weakened resistance, such as infants and the elderly. Since inhibition of microbial proliferation is an important aspect of sanitary and comfortable living, it has become desirable to provide antimicrobial functions for a wide variety of common medical products, subsistence goods and clothing.
Synthetic resins are preferred as materials to be used for medical products, subsistence goods, clothing and the like because they are lightweight, strong and can be freely shaped according to the purpose. Most synthetic resins, however, do not by themselves exhibit antimicrobial functions. It has therefore been common to add various antimicrobial agents to synthetic resin molded articles in order to impart antimicrobial functions.
Methods which have been developed to impart antimicrobial properties to synthetic resins and the like include methods of adding compounds containing metals such as silver, gold and zinc to synthetic resins, and methods of adding zeolite-based solid particles ion-exchanged with silver ions or copper ions to synthetic resins.
However, such synthetic resin molded articles can also produce dermopathies in individuals depending on the purpose of use, and particularly in infants with weaker skin resistance or in allergic-prone individuals.
Other methods involve addition of highly safe naturally-derived antimicrobial compounds to synthetic resins. As such naturally-derived antimicrobial compounds there may be mentioned allyl isothiocyanates extracted from mustard or horseradish, protamines extracted from mature testicles of salmon, trout or the like, chitosan obtained by deacetylation of chitin extracted from crustaceans, and ε-polylysine obtained from microbes belonging to the genus Streptomyces. 
However, although these naturally-derived antimicrobial compounds are highly safe, allyl isothiocyanates are volatile and therefore readily volatilize by heat during production of synthetic resin molded articles, and consequently they must be used in large amounts in order to impart an adequate antimicrobial function to antimicrobial synthetic resin molded articles, while protamines, being proteins, are poorly resistant to heat and therefore cannot withstand the working temperatures of synthetic resins. Also, chitosan is poorly soluble in solvents, and therefore without modification it is troublesome to use in synthetic resins.
ε-Polylysine is a polymer compound comprising lysine groups bonded together by acid amide bonds between the ε-amino groups and the hydroxycarbonyl groups of adjacent lysines. ε-Polylysine is highly stable, being a polymer of the essential amino acid lysine, and its high cation content gives it unique antimicrobial and other properties. Furthermore, because it is a polymer it has very low volatility and exhibits heat resistance. However, it is water-soluble and therefore has low solubility in solvents other than water and some alcoholic solvents.
Methods for modifying naturally-derived antimicrobial compounds include introduction of myristoyl groups into chitosan to enhance the emulsification properties (see Technical Document 1), and modification of protamines or ε-polylysine with dextran to enhance their emulsifying activity (see Technical Document 2). However, these methods are intended to impart or improve emulsification properties for naturally-derived antimicrobial compounds, and they do not improve the volatility, heat resistance or solubility in organic solvents, nor do they improve compatibility with resins. Needless to mention, because such compounds do not include silicone chains they do not exhibit the properties of silicone.
Polyorganosiloxanes can be blended with or copolymerized with various organic resins such as thermoplastic resins, thereby imparting the properties of polyorganosiloxanes such as weather resistance, surface water repellency, lubricity, low abrasiveness, biocompatibility, antithrombotic properties and gas permeability for efficacy as organic resin modifiers, and their uses in paints, adhesives, coating agents, fiber processing agents, inorganic material surface modifiers, toiletries, cosmetics and the like are known.
Naturally-derived antimicrobial compounds such as ε-polylysine are water-soluble and are therefore almost always used in aqueous systems and almost never employed in oil-based systems. On the other hand, polyorganosiloxanes are generally lipophilic and are therefore virtually insoluble in water. Certain types of polyorganosiloxanes which are water-soluble or have high affinity for water are known, however, such as non-ionic polyorganosiloxanes modified with polyethylene glycol or the like. Nevertheless, virtually no polycationic water-soluble polyorganosiloxanes or antimicrobial polyorganosiloxanes are known. Thus, while naturally-derived antimicrobial compounds such as ε-polylysine have been blended together with polyorganosiloxanes for their simultaneous use, it has been very difficult to achieve mixtures of the two. A third component such as a surfactant has therefore been necessary, thus requiring advanced emulsifying techniques. This has placed restrictions on the means currently employed for uniform mixing of naturally-derived antimicrobial agents, polyorganosiloxanes and resins.
The prior arts are disclosed in JP-A 54-147220/1979, JP-A 59-133235/1984, Japan Cosmetic Journal, Vol.26, No.2(2002), Foods Food Ingredients J. Jpn. No.185(2002).